Hi Raj,

I don't know why it is said that CTLE cannot equalize precursor ISI in INPHI slides. Probably in their specific project, that CTLE is not enough. Anyway, I think it does equalize precursor ISI because a high-pass filter makes the the rising edge more charp in time domain.

And in slide 14 of the link below
http://www.ece.tamu.edu/~spalermo/ecen689/lecture8_ee720_rxeq.pdf,
the 6Gb/s input opens eye with a CTLE. Obviously it equalize precursor ISI because the edge of input data becomes more sharp, otherwise the eye is closed.

Best Regards,
Yawei

@bharat, Interesting question about why there is usually more postcursor than precursor.

First of all, I think mathematically it is always possible to come up a channel which has more precursor. But for a physical cable, I guess one qualitative explanation can be as following:

There are two main loss mechanism in a cable channel: skin effect and dielectric loss. The first one causes only post cursor and the second one causes almost symmetric precursor and post cursor. The overall loss is convolution of the two losses. Therefore, qualitatively, more postcursor exists in physical cable.
A good explanation about these two loss mechanism is covered in this paper:  
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1610643  

Of course, this explanation is still hand-waving. Hope some expert can give more intuitive answer.